Liquid crystal display apparatus

ABSTRACT

In one pixel, a stepped difference portion having an inclination degree a/b is formed on an alignment control layer, the alignment control layer is made of a material in which a liquid crystal alignment capability is given according to a polarization light radiation, and according to the polarization light radiation the liquid crystal alignment capability is added in the vicinity of the stepped difference portion. A thick and transparent organic high molecular layer is interposed between the alignment control layer and a substrate and a close adhesion characteristic and a transparency characteristic can be made compatible therewith. Accordingly, a problem in which the manufacturing margin in an alignment processing is narrow can be solved, and generation of a display failure according to a fluctuation in the initial alignment direction can be reduced. In this way, a large size liquid crystal display apparatus having a high quality and in which the contrast ratio is heightened can be provided.

TECHNICAL FIELD

The present invention relates to an in-plane switching (In-planeswitching: IPS) system liquid crystal display apparatus in which theelectric field is applied to a liquid crystal layer in substantiallyparallel direction against a substrate and a liquid crystal displayapparatus is operated, in particular relates to a large size panel usestructure having a good productivity of an alignment control layer.

BACKGROUND TECHNIQUE

A strong need for a large size, a wide viewing angle and a multi-colorperformance of a screen size of a liquid crystal display apparatus isheightened. As to a viewing angle characteristic necessary for the largesize, many definitions exists which are as a range in which a half-tonelevel is not reversed, a range in which a brightness, a contrast ratio,and a color tone are not varied, etc.. In the multi-color display, it isnecessary to heighten a respective color re-production and further it isnecessary to improve drastically the viewing angle characteristicaccording to the above stated definitions. As the liquid crystal displaybeing compatible with the wide viewing angle and the large screen, ithas proposed a combination system (IPS-TFT-LCD) in which IPS liquidcrystal and a thin layer transistor (Thin layer transistor TFT) (Oota etal, Proceeding of the Fifteenth International Display ResearchConference (Asia Display '95; p.707) and a practical use of a monitorsystem in which a display screen size has diagonal 13.3 inches(corresponded to 15 type CRT) has started (Kondo et al, SID '96 DigestNo.8.1).

However, to realize the practical use of IPS-TFT-LCD corresponded to ascreen larger than more than 17 type which will be a main current in CRTafter this, it is necessary to develop a large size panel use newstructure and process. In the conventional technique, it does not referto a method for adding a homogeneous alignment characteristic in a panelhaving a stepped difference structure which is a subject mater of thepresent invention.

In IPS-TFT-LCD, it accompanies the difficulty of an alignmentprocessing. A margin of this is narrow remarkably in comparison with aconventional type TN (Twisted Nematic) system, in particular in normallyopen type TN system (at a low voltage side a bright display, at a highvoltage side a dark display). The reasons for the narrow margin arethree points of following items (1)-(3).

(1) Stepped Difference Structure

In IPS-TFT-LCD, in principle it is necessary to arrange many long andnarrow electrodes (at the case may be, it is called as an inter digitalelectrode) having several microns order degree.

Accordingly, a fine stepped difference structure is formed. A largenessof the stepped difference is determined by a thickness of the electrodesand shapes of various kinds of layers which are formed on theelectrodes, in ordinary it has more than 0.1 micron. At the most upperlayer of these layers, a high molecular layer such as polyimide isformed as an alignment control layer (it is called as an alignmentlayer). In the conventional mass-production technique, a surface of thisalignment control layer is carried out according to a rubbing processingand a liquid crystal alignment ability is added. On the other hand, therubbing use cloth is constituted by binding narrow fibers having athickness of 10-30 microns degree, substantially since every one narrowfiber gives the sharing force in a predetermined direction to a localportion of the alignment layer, a processing for adding the liquidcrystal alignment ability is carried out. As the fibers, there is anextremely narrow fiber having several microns degree, however as therubbing use fiber, however since the rigidity for adding the some degreefriction force is required, it has not used practically. Since anelectrode interval in IPS system is 10-30 micron degree same to that ofa diameter of the above stated fiber, the rubbing at a vicinity of thestepped difference is not carried out fully, as a result the alignmentis disturbed easily. The disturbance in the alignment causes a loweringin a picture quality such as a rise of a black level and a lowering inthe contrast ratio according to the above stated rise, and anon-homogeneity in the brightness.

As a method for solving the above stated problems, it has proposed amethod for flattening a surface of the alignment layer, however thecomplete flattening manner invites following the side effects and thismethod is not used practically. A first is a problem which is caused bya phenomenon in which a spacer for controlling a liquid crystal layer atconstant is moved easily. By the move of the spacer, a spacerdistribution becomes up homogeneously and a liquid crystal layerthickness becomes non-homogeneously, accordingly the non-homogeneity ofthe brightness is invited. Further, during the spacer move the surfaceof the alignment layer is hurt and it causes a light leakage. From thesepoints, it is necessary to have some degree stepped difference. Further,to solve the problem about the spacer move, it is desirable to form thestepped difference on one of a pair of substrates, in a case where TFTside is flattened and the stepped difference is tried to form to anopposite substrate side, it is necessary to pay an attention. In IPSsystem, to apply the effective in-plane switching, it is necessary toform, many thin and narrow shape inter digital electrodes, as a resultmany stepped differences are formed on the TFT side substrate. Todissolve the stepped differences it is effective to coat thick anorganic high molecular layer, however when the thick insulation layer isformed on the electrode, it invites a lowering of the effective voltagewhich applies to the liquid crystal. As a result, a threshold voltagebecomes high and it causes a problem in which since it is necessary touse driver having a high pressure withstand a consumption electric powerbecomes high. It is realistic to form the insulation layer having aproper thick to the TFT side substrate and to remain a proper steppeddifference. As shown in FIG. 1, it is necessary to form a ratio a/dbetween the liquid crystal layer thickness d and the stepped differencea at least more than 0.02. In particular, for example, to drive thelarge size panel having diagonal size more than 18 inches, to restrain adeterioration of the voltage waveform from a driver LSI, it is necessaryto lower the resistance value of the electrode, accordingly theelectrode is necessarily to be formed thick. In the large scale panel,the stepped difference remains necessarily.

(2) Alignment Angle

In IPS-TFT-LCD, it is necessary to establish in principle an initialalignment direction to arrange a direction to which the electrode isextended, or by shifting with more than a constant angle from a verticaldirection of the above stated direction. Herein, the electrode indicatesa signal wiring electrode, a common electrode and a pixel electrode in apixel. To regulate the initial alignment direction by the rubbingmethod, as stated in above, it is necessary to rub to a predeterminedangle direction by the fibers having about 10-30 microns degree, by thestepped difference between the wiring being extended to the constantdirection such as the signal wiring electrode, the common electrode inthe pixel, and the pixel electrode in the pixel and the end portionsthereof, it causes a problem in which the fibers are drawn into to thestepped difference direction from the design angle.

(3) Profound Degree of the Black Level

As one of the characteristics of IPS-TFT-LCD, it can enumerate that theprofound of the black level (the black display) is good. Accordingly,the disturbance in the alignment comes to the fore in comparison withother systems.

In the conventional normally open type TN system, the dark level isobtained by the condition to which the high voltage is applied. In thiscase, under the high voltage almost liquid crystal molecular are allpresent to the electric field direction which is a vertical onedirection to the substrate face, with the relationship between theliquid crystal molecular arrangement and a polarizing plate arrangement,the dark level can be obtained. Accordingly, the homogeneity of the darklevel does not depend in principle on the initial alignment conditionduring the low voltage time. Further, the eyes of the human recognizesthe roughness of the brightness as a relative ratio and further reactsnear with a logarithms scale, accordingly it is sensitive to afluctuation of the dark level. From the above stated view points, in theconventional normally open type TN system in which the liquid crystalmolecular is arranged compulsively to one direction under a highvoltage, it is insensitive to the initial alignment condition and it isin a better position than. On the other hand, in the in-plane switchingsystem, to display the dark level at the low voltage or at the voltageof zero, it is sensitive to the disturbance of the initial alignmentcondition. In particular, an arrangement (it is called as abi-refraction mode) in which a homogenous arrangement where the liquidcrystal molecular alignment direction is in parallel each other on anupper substrate and a lower substrate is formed and also a lighttransmission axis of one polarizing plate is formed in parallel to theliquid crystal molecular alignment direction and that of anotherpolarizing plate is formed in orthogonally, in a polarization lightwhich is incident to the liquid crystal layer a linear polarizing lightis propagated without the disturbance. This is effective to be profoundin the dark level.

A transmission rate T of the bi-refraction mode is expressed by afollowing formula (1).

T=To×sin²{2θ(E)}×sin²{Π×deff ×Δn/λ}.  (1)

Herein, To is a coefficient and is a numeral value which is determinedmainly by a transmission rate of the polarizing plate used in the liquidcrystal panel, θ(E) is an angle making by the alignment direction (aneffective light axis of the liquid crystal layer) of the liquid crystalmolecular and the polarization light transmission axis, E is anapplication electric field strength, deff is an effective thickness ofthe liquid crystal layer, Δn is a refraction rate aeolotropiccharacteristic, and λ is a wavelength of the light. Further, herein, aproduct the effective thickness deff of the liquid crystal layer by therefraction rate aeolotropic characteristic Δn, namely (deff×Δn), iscalled as a retardation. Further, the thickness deff of the liquidcrystal layer is not a whole thickness of the liquid crystal layer butwhen the voltage is applied it indicates a thickness of the liquidcrystal layer for changing practically the alignment direction. Becausethe liquid crystal molecular at a vicinity of an interface of the liquidcrystal layer does not change the alignment direction when the voltageis applied according to an affect of an anchoring of the interface.Accordingly, when the thickness of the whole liquid crystal layer whichis sandwiched by the substrates is expressed by dLC, between thisthickness dLC and the thickness deff, it has always a relationshipdeff<dLC and this difference differs from the liquid crystal materialused in the liquid crystal panel, and the interface for contacting theliquid crystal layer, for example, the kinds of the alignment layermaterials, and it can be estimated to have in general 20-40 nm degree.

As clearly understood from the above stated formula (1), the matter fordepending to the electric field strength is sin²{2θ(E)} item and bychanging angle θ in response to the electric field strength E thebrightness can be adjusted. To form the normally close type, under thevoltage non-application time, since the polarizing plate is establishedto have θ=0 degree, it works to be sensitive to the disturbance of theinitial alignment direction.

(4) Problems of the Photo-alignment Method

As explained in a latter portion, as to the problems from (1) to (3), itis possible to solve by an introduction of the photo-alignment method inplace of the conventional rubbing method. The photo-alignment method isclassified largely a photo-dissolution type and a photo-reaction type.In both cases, from a practical use there are following problems. Toperform the close adhesion characteristic improvement between thealignment layer material and the substrate it is necessary to have somedegree thickness, however in this case it is difficult to have thecompatibility between the photo-reaction characteristic and thetransparency characteristic. In a case the bad coloring is invited andthe utilization efficiency of the light and the picture quality lower.The assurance between the close adhesion characteristic between thealignment control layer and the substrate is important in the practicaluse, and the success or the failure of the photo-alignment is essential.

Further, as stated in above, to adopt the photo-alignment to thesubstrate having the stepped difference structure, it is necessary topay consideration to the following points. In the photo-alignmentmethod, to a whole face of the alignment layer, the light having anability for reforming a surface, for example as the ultra-violet light,is irradiated, in this case since the reflection of the light is causedat the stepped difference portion, it is necessary to pay considerationto the light course. It is desirable to have a modulated and inclinedtaper structure as the stepped difference. In a case when the ratio a/bof the parameter shown in FIG. 1 is less than 1 (in the inclinationangle, less than 45 degree), the refection light at the taper portion isnot reached to a pixel portion, accordingly it does not cause thealignment failure.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide in particular a largesize liquid crystal display apparatus wherein the problem in which amanufacture margin is narrow in an alignment processing being a specificproblem in IPS-TFT-LCD stated in above can be solved and a high qualitypicture quality in which a contrast ratio is heightened can be obtainedand a generation of a display failure according to a fluctuation of aninitial alignment direction can be reduced.

According to the present invention, in an active matrix type in-planeswitching liquid crystal display apparatus in which at least one of apair of substrates is transparent, a thickness of a liquid crystal layeris controlled to have a substantially constant thickness by a spacerwhich is dispersed and sandwiched between the pair of substrates, on asurface at a side for contacting at least one liquid crystal layer ofthe pair of substrates, an inclination degree a/b of a steppeddifference portion having an alignment control layer which is formed ona surface of a display pixel is less than 1, and the alignment controllayer is made by a material which is enable to give a liquid crystalalignment ability according to a polarization light radiation, and theliquid crystal alignment ability has at a vicinity of the steppeddifference portion.

According to the present invention, during the formation of thealignment control layer of the panel having the stepped differencestructure the manufacture margin can be enlarged and as a result it ispossible to provide the large size liquid crystal display apparatus inwhich the initial alignment direction is formed homogeneously and thehigh quality picture quality can be obtained. In the conventionalrubbing method, the end portion of the stepped difference works as aguide of the rubbing use cloth fibers and the fibers are drawn into theextension direction of the stepped difference and to the corner portionsof the stepped difference the fibers do not reach, accordingly it isimpossible to carry out the alignment processing and the alignmentfailure causes. On the other hand, according to the present invention,since the alignment ability is added by the polarization lightradiation, in regardless the shapes the polarization light having theconstant direction can be radiated to the minute portions, as a resultthe liquid crystal alignment direction is formed homogeneously. Further,the stepped difference structure can be formed at the substrate sidehaving the electrodes group or at the opposed side substrate in which incommonly the color filter is formed. In particular, when the blackmatrix formed to the boundary portion of the color filter is made by theresin material and the black color paints, to make thicker this blackmatrix portion than the pixel portion in which the light is transmitted,the stepped difference is formed easily, and the present invention canwork effectively. In reversely, when the black matrix is made by themetal thin layer material such as chromium, the black matrix portionbecome thin relatively. In this case, also the present invention canwork effectively. Further, IPS liquid crystal, as clearly understoodfrom the formula (1), since the liquid crystal layer thickness deff forgiving the maximum transmission rate differs from every the waveform λof the light, and since the stepped difference is caused in a case wherethe liquid crystal thickness deff is changed at every color of the colorfilter, the present invention can work effectively. Further, when thedielectric rate aeolotropic characteristic is positive and also theangle making by the alignment direction of the electric fieldnon-application time on the alignment control layer and the electricfield direction is 45-88 degree and when the dielectric rate aeolotropiccharacteristic is negative and also the angle making by the alignmentdirection of the eclectic field non-application time on the alignmentcontrol layer and the electric field direction is 2-45 degree, inparticular the present invention can work effectively.

Further, according to the present invention, in an active matrix typein-plane switching liquid crystal display apparatus in which between ina pair of substrates which at least one is transparent the liquidcrystal layer is sandwiched, it is effective when the spacer having theregularity characteristic to the non-transparent portion of the pixel isformed in place of the dispersed spacer. In this spacer having theregularity characteristic can be formed, for example, according to aphoto-lithography process. Naturally, since the spacer exists, it isnecessary to form the stepped difference having the large size such as2-5 microns degree and it is difficult to adopt the rubbing method.

Further, in particular it is necessary to pay the consideration aboutthe problems of the close adhesion characteristic between thephoto-reaction type alignment layer material and the substrate and thecoloring characteristic. As to those problems, it can be solved by theintervene the transparent organic high molecular layer having thethickness thicker than the alignment control layer between the alignmentcontrol layer and the substrate. It is a desirable to have a value of0.2-3 microns as the thickness of the transparent organic high molecularlayer and it is a desirable to have a value of 0.01-0.1 microns as thethickness of the alignment control layer. The close adhesioncharacteristic is further strengthened by the addition of the adhesionpromotion agent for heightening the close adhesion characteristic of thesubstrate face and the alignment control layer to the organic highmolecular layer. Since the organic high molecular layer has some degreethickness, this works to reduce the deterioration caused by thetemperature change etc. Further, more desirably when both of thealignment control layer and the transparent organic high molecular layerare made of polyimide, since they are the same system materials, theclose adhesion characteristic can be further strengthened. When thetransparent organic high molecular layer is made by amorphous material,since the whole face of the layer face presents homogeneous state, thereduction in the deterioration and the improvement in the close adhesioncharacteristic can be obtained. Further, to form thick the above statedtransparent organic high molecular layer, polyamic acid having theconcentration of more than 8% is coated, after that it is desirable toheat the temperature where the imization proceeds some degree, and toform thin the alignment control layer after soluble polyimide orpolyamic acid has coated, it is desirable to heat the temperature wherethe solvent agent evaporates. In case of polyamic acid, it is desirableto rise to the temperature where the imization proceeds.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a view showing an insulation layer, a transparent organic highmolecular layer, an alignment control layer in which a portion of aschematic cross-sectional view of FIG. 2 is enlarged.

FIG. 2 is a view showing a cross-sectional view of a cell of a liquidcrystal display apparatus according to the present invention.

FIG. 3 is a view showing an angle by making a respective liquid crystalmolecular long axis alignment direction against to an electric fielddirection and a respective polarizing plate polarization lighttransmission axis.

FIG. 4 is a schematic view showing an operation principle of the liquidcrystal in an in-plane switching system liquid crystal displayapparatus.

FIG. 5 is a schematic view showing a plan view and a cross-section of anarrangement of an electrodes group of a unit pixel portion shown inEmbodiment 1, an insulation layer, and an alignment control layer.

FIG. 6 is a view showing an example of a circuitry system structure in aliquid crystal display apparatus according to the present invention.

FIG. 7 is a view showing an example of an optical system structure in aliquid crystal display apparatus according to the present invention.

FIG. 8 is a view showing one example of a structure in which a steppeddifference is provided at a color filter side according to the presentinvention.

FIG. 9 is a view showing another example of a structure in which astepped difference is provided at a color filter side according to thepresent invention.

FIG. 10 is a view showing one example of a structure in which a spaceris formed to have the regularity to a non-transparent portion of apixel.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a concrete construction of embodiments will be explained.

Embodiment 1

In FIG. 2, a schematic cross-sectional view of a cell of a liquidcrystal display apparatus of this embodiment is shown. Between a pair oftransparent substrates 1, 1′ is sandwiched by a liquid crystal layer 32in which plural compounds are composed. In FIG. 2, it showsschematically by a rod shape liquid crystal molecular 5. On both outersides of the pair of substrates 1, 1′, polarizing plates 9, 9′ arearranged. On a face of a cell inner side of one substrate 1 stripe shapeelectrodes 2, 3 are formed, on the above this an insulation layer 4 isformed, further on the above this an alignment control layer 8 isformed. The electrode 2 is a common electrode to which a constantwaveform voltage which does not depend on an image signal is applied,and the electrode 3 is a pixel electrode in which the waveform changesto in response to the image signal. Further, at the same height of thepixel electrode 3 an image signal electrode 10 is arranged. Both thethicknesses of the pixel electrode 3 and the image signal electrode 10are 0.2 microns. The insulation layer 4 has two layers and each oflayers comprised of silicon nitride layer and both the thickness are 0.4microns. To the opposed another substrate, a color filter 5 for carryingout the color display is formed.

FIG. 1 is a schematic view in which a layer construction at a peripheryof the electrode group shown in FIG. 2 is shown in detail. On theinsulation layer 4 which covers the electrodes 3, 10 a transparentorganic high molecular layer 7 is coated, further on the above this thealignment control layer 8 is coated. The thickness of the transparentorganic high molecular layer and the alignment control layer is 0.2microns and 0.03 microns, respectively. A stepped difference a is 0.25microns. Further, a width b of a taper portion is 0.35 microns, a ratioa/b is 0.71. A thickness d of the liquid crystal layer is 4.0 microns, aratio a/d is 0.0625.

As the transparent organic high molecular layer, the polyamic acidsolution of PIQ-1800 made by Hitachi Chemical Company Ltd. which is theamorphous layer having the concentration of 8.5% is coated, after thesolvent agent is dried by heating to the temperature 150° C. during 10minutes and polyamic acid solution being a precursor of the alignmentcontrol layer 8 and having the concentration 3% is coated. To thepolyamic acid solution made by Hitachi Chemical Company Ltd., as anadhesion promotion agent, 2 weight % γ-amino propyl thriethoxy silane ismixed. Further, as the adhesion promotion agent for promoting the closeadhesion characteristic, it is not limited to this but followingmaterials can be employed. For example, 4-amino phenoxy dimethyldimarthy vinyl silane, amoni methyl trimethy silane, 2-amino propyldimethyl ethoxy silane, 3-amino propyl dimethyl ethoxy silane, methyltris (2-amino ethoxy) silane, 3-amino propyl diethoxy methyl silane canbe employed. After that the braking at 200° C., during 30 minutes iscarried out and the imidization is carried out. Further, the precursorof the alignment control layer 8 is polyamic acid being the polyimideprecursor and as the monomer component as diamine compound matter inwhich a chemical formula 1 including diazobenzene groups and 4-4′diamino diphenyl methane etc. is mixed with an equal mol ratio is usedand to dianhydride compounds pyromellic dianhydride and 1, 2, 3, 4-cyclobutane-tetracarboxylic dianhydrides as the polyamic acid is composed.

Further, in this embodiment, azobenzene groups as described in U.S. Pat.No. 4,974,941 is introduced and photo-isomerization reactioncharacteristic is added, however it is not limited this however it canemploy a substance having photo-isomerization reaction characteristicand the liquid crystal alignment is controlled. For example, such as astilbene groups can be employed. In this embodiment, after two layerspolyimide precursor layer has formed, the imidization is carried outaccording to the heat baking. After that, high molecular beads which aredispersed in methanol and have a particle diameter of 4.2 microns aredispersed in a solution condition. Since the dispersion medium isalcohol, it can evaporate within one minute and only spacer beads areremained. The dispersion density is about 100 numbers per 1 mm². Afterthat, the upper and lower substrates are overlapped and are assembled toan empty cell condition using a sealing member to a peripheral portion.

After that, under a high pressure mercury lamp having a peak of thewavelength of 436 nm as a light source, a polarization light is radiatedfrom an outside of a cell through a polarization film which transmitsthe light having the wavelength of 400 nm. A radiation luminous energyis about 2J/cm². After that, the liquid crystal composition matter isencapsulated under the room temperature, further after that an annealingat 100° C. and during 10 minutes is carried out, the liquid crystalalignment is obtained to a substantially vertical direction against tothe above stated radiation polarization direction. As to the liquidcrystal molecular long axis at the obtained alignment condition, anangle ΦLC which is defined in FIG. 3 is 75 degrees. As stated in above,the liquid crystal display apparatus having the thickness d of theliquid crystal layer of 4.0 μm can be obtained. As the liquid crystalcomposition, nematic liquid crystal in which the dielectric aeolotropiccharacteristic is positive. A value of Δ∈ is 10.2 and the refractionratio aeolotropic characteristic Δn is 0.073.

FIG. 4 shows a switching principle of the liquid crystal molecular inthe panel obtained by the above. In this embodiment, as to the liquidcrystal molecular 6, during the electric field non-application time,against to the vertical direction to the longitudinal direction of thestripe shape electrode, it is formed ΦLC=75 degrees, however when thedielectric rate aeolotropic characteristic is positive, it can be formed45 degrees≦ΦLC<90 degrees. As the liquid crystal composition shown inFIG. 4, it can be formed with the dielectric aeolotropic having thenegative. In this case, the initial alignment condition is aligned to 0degree≦ΦLC<45 degrees from the vertical direction of the stripe shapeelectrode. In FIG. 4, an alignment direction 11 is shown with an arrowmark. Next, as shown in FIG. 4(b), (d), between the electrodes 2, 3 theelectric field 13 is applied, to arrange the direction of the electricfield 13 to the molecular long axis in parallel the liquid crystalmolecular 6 changes the direction. In this time, θ in the formula (1) ischanged in response to the electric field strength E and then thetransmission rate is changed.

In this embodiment, since the display system having bi-refraction modeis employed, the liquid crystal is sandwiched between the orthogonalpolarizing plates. Further, to obtain the normally open typecharacteristic which presents the dark display at the low voltage, thepolarization transmission axis of one polarizing plate is formedorthogonal to the initial alignment direction. The transmission lightstrength to be observed is determined by the formula (1).

FIG. 5 shows an arrangement of the electrodes group, the insulationlayer, the alignment control layer in the unit pixel according to thepresent invention. FIG. 5(a) is a front view which is viewed from thevertical direction to the panel face, FIGS. 5(b), (c) are views showinga side face cross-section.

FIG. 6 shows a circuitry system structure in the liquid crystal displayapparatus according to this embodiment. The apparatus is constituted bya vertical scanning signal circuit 17, an image signal circuit 18, acommon electrode drive use circuit 19, a power supply and a controller20, however the present invention is not limited to this structure.

FIG. 7 shows an optical system system structure in the liquid crystaldisplay apparatus according to this embodiment. To a back face of aliquid crystal panel 27, a back-light unit 26 is provided, such unit iscomprised of a light source 21, a light cover 22, a photo-conductivebody 23, and a diffusion plate 24. Herein, a prism sheet 25 forincreasing a front face brightness is provided, however the provision ofthis sheet takes no notice. Preferably, this sheet can be omitted fromthe reduction of the viewing angle dependency characteristic of thebrightness.

With the above stated structure, IPS-TFT-LCD having the diagonal angleis 13.3 inches, the pixel number of 1.024×RGB×768 is manufactured fortrial, the contrast ratio exceeds over 300 extending over a whole faceand further the liquid crystal display apparatus having a good displayhomogeneity characteristic can be obtained.

Comparison Example

This example differs merely that in place of the photo-alignment methodas the photo-alignment control method in Embodiment 1, the rubbingmethod is used. As the monomer component, as diamine compounds, 4-4′diamine diphenyl methane is used but the material having thephoto-reaction characteristic is not used.

With the above structure, when IPS-TET-LCD having the same size toEmbodiment has manufactured in trial, the light leakage accompanyingwith the disturbance of the alignment has observed at the steppeddifference portion. As a result, the non-homogeneity of the contrastratio has observed and in the low portion it is 80 and at the highportion it has remained 180 degree.

Embodiment 2

Against to Embodiment 1, following points differ.

On the other substrate which is arranged oppositely to the substratehaving the electrodes group, the stepped difference structure is added.Further, to this opposite substrate the color filter is formed and atthe boundary portion of the three primary colors being red (R), yellow(Y) and blue (B) the black matrix being a mixture matter of the resinmaterial and the black color paints is formed. The structure is shown inFIG. 8. The thickness of the black matrix is thicker than all of theprimary colors color filter portion. On the black matrix and the primarycolors color portion, similarly to the electrode side substrate ofEmbodiment 1, the alignment control layer 8 which is added the liquidcrystal alignment ability according to the transparent organic highmolecular layer 7 and the polarization light radiation is coated.Further, as explained in the formula (1), since the liquid crystal layerthickness for giving the maximum transmission rate differs every color,in this embodiment to make thin the liquid crystal layer of the bluepixel which utilizes the light having the short wavelength the thicknessof the color filter is formed thick with 0.02 microns degree. In thiscase, the stepped difference a at the surface of the alignment controllayer 8 is 0.5 microns at maximum. Further, the width b of the taperportion is 0.6 microns and the ratio a/b is 0.83. The thickness d of theliquid crystal layer is 3.3 microns and the ratio a/d is 0.15.

With the above structure, in similarly when IPS-TFT-LCD having thediagonal angle is 13.3 inches, the pixel number of 1.024×RGB×768 ismanufactured for trial, the contrast ratio exceeds over 300 extendingover a whole face and further the liquid crystal display apparatushaving a good display homogeneity characteristic can be obtained.

Embodiment 3

In Embodiment 2, the thickness of the black matrix is thicker than allof the primary colors color filter portion, but in this embodiment inreversely the black matrix portion is formed to have the most thinportion. The other points except the above are same to Embodiment 2. Asto the black matrix use material, a low reflection type three layerschromium layer is used. In this case, the stepped difference a at thesurface of the alignment control layer 8 is 0.15 at the maximum.Further, the width b at the taper portion is 0.8 and the ratio a/b is0.19. The thickness d of the liquid crystal layer is 4.2 microns and theratio a/d is 0.036.

With the above structure, in similarly when IPS-TFT-LCD having thediagonal angle is 13.3 inches, the pixel number of 1.024×RGB×768 ismanufactured for trial, the contrast ratio exceeds over 300 extendingover a whole face and further the liquid crystal display apparatushaving a good display homogeneity characteristic can be obtained.

Embodiment 4

In Embodiments 1-3, as the spacer the high molecular beads are obtainedby the dispersion, but in this embodiment, according to thephoto-lithography process on the black matrix the pillars having theheight of 2.9 microns with the regularity. The maximum steppeddifference a of the pixel portion is 0.15 microns. Further, the width bof the taper portion is 0.20 microns and the ratio a/b is 0.75. Thethickness d of the liquid crystal layer is 2.9 which is same to that ofthe height of the pillar and the ratio a/d is 0.052.

With the above structure, in similarly when IPS-TFT-LCD having thediagonal angle is 13.3 inches, the pixel number of 1.024×RGB×768 ismanufactured for trial, the contrast ratio exceeds over 300 extendingover a whole face and further the liquid crystal display apparatushaving a good display homogeneity characteristic can be obtained.

According to the present invention, the problem where manufacture marginof the alignment processing is narrow, this is the specific problem inIPS-TFT-LCD in which to the substrate the electric field is applied inthe substantial parallel direction and the liquid crystal is operatedcan be solved. Further, at the same time it is possible to provide theliquid crystal display apparatus having the high picture quality inwhich the generation of the display failure according to the fluctuationof the initial alignment direction can be reduced. Accordingly, inparticular it is possible to provide the practical use of the large sizehigh picture quality liquid crystal display apparatus.

What is claimed is:
 1. A liquid crystal display apparatus comprising: apair of substrates, at least one of which is transparent; a liquidcrystal layer arranged between said pair of substrates; a plurality ofelectrodes formed on one substrate of said pair of substrates forapplying an electric field substantially in parallel to a face of saidsubstrate, and plural active elements connected to these electrodes; analignment control layer formed on a face of at least one of said pair ofsubstrates and being in contact with said liquid crystal layer; andoptical means for changing an optical characteristic in response to amolecular alignment condition of said liquid crystal layer; wherein thethickness of said liquid crystal layer is set to a substantiallyconstant thickness by spacers, which are dispersed and sandwichedbetween said pair of substrates, and a surface of the alignment controllayer on said at least one of said pair of substrates which is incontact with said liquid crystal layer has stepped difference portions;on a surface formed in a display pixel, an inclination degree of astepped difference portion in said alignment control layer is less than1, and said alignment control layer is made of a material which is ableto give a liquid crystal alignment capability according to apolarization light radiation in a vicinity of said stepped differenceaccording to said polarization light radiation.
 2. A liquid crystaldisplay apparatus according to claim 1, characterized in that a ratioa/d between a height a of said stepped difference portion and athickness d of said liquid crystal layer has a range of 0.02-1.
 3. Aliquid crystal display apparatus according to claim 1 or claim 2,characterized in that said substrate having said surface in which saidstepped difference portion is formed within said pair of substrates isthe substrate having said plurality of electrodes.
 4. A liquid crystaldisplay apparatus according to claim 1 or claim 2, characterized in thatsaid substrate having said surface in which said stepped differenceportion is formed within said pair of substrates is the other substratewhich is arranged opposite to said substrate having said plurality ofelectrodes.
 5. A liquid crystal display apparatus according to claim 4,characterized in that on said other substrate a color filter havingplural different colors is formed.
 6. A liquid crystal display apparatusaccording to claim 5, characterized in that said stepped differenceportions are formed in the vicinity of a black matrix which is formed ona boundary of said color filter having plural different colors.
 7. Aliquid crystal display apparatus according to claim 6, characterized inthat said black matrix is comprised of a resin material and black colorpaints and has a thickness greater than the thickness of a pixel portionin which the light is transmitted.
 8. A liquid crystal display apparatusaccording to claim 5, characterized in that a liquid crystal layerthickness of said pixel portion differs from the thickness of said colorfilter having plural different colors.
 9. A liquid crystal displayapparatus according to claim 1 or claim 2 characterized in that adielectric rate aeolotropic characteristic of said liquid crystal layeris positive, and an angle forming an alignment direction with anelectric field direction during an electric field non-application timeof said alignment control layer of said liquid crystal layer is 45-88degrees.
 10. A liquid crystal display apparatus according to claim 1 orclaim 2 characterized in that a dielectric rate aeolotropiccharacteristic of said liquid crystal layer is negative, further anangle forming an alignment direction with an electric field directionduring an electric field non-application time of said alignment controllayer of said liquid crystal layer is 2-45 degrees.
 11. A liquid crystaldisplay apparatus, comprising: a pair of substrates, at least one ofwhich is transparent; a liquid crystal layer arranged between said pairof substrates; a plurality of electrodes formed on one substrate of saidpair of substrates for applying an electric field substantially inparallel to a face of said substrate, and plural active elementsconnected to these electrodes; an alignment control layer formed on aface of at least one of said pair of substrates and being in contactwith said liquid crystal layer; and optical means for changing anoptical characteristic in response to a molecular alignment condition ofsaid liquid crystal layer; wherein the thickness of said liquid crystallayer is set to a substantially constant thickness spacers, which areformed in a non-transparent portion of a pixel; on a surface formed in adisplay pixel, an inclination degree of a stepped difference portion insaid alignment control layer is less than 1, and said alignment controllayer is made of a material which is able to give a liquid crystalalignment capability according to a polarization light radiation insubstantially the whole of a display area in the vicinity of saidstepped difference according to said polarization light radiation.
 12. Aliquid crystal display apparatus according to claim 11, characterized inthat said spacers are formed according to a photo-lithography process.13. A liquid crystal display apparatus according to claim 12,characterized in that said spacers are formed on a black matrix.
 14. Aliquid crystal display apparatus according to any one of claims 1, 2,11, 12 and 13, characterized in that said alignment control layer has aphoto-isomerization reaction characteristic.
 15. A liquid crystaldisplay apparatus according to claim 14, characterized in that saidalignment control layer has one of azobenzene groups and stilbenegroups.
 16. A liquid crystal display apparatus according to claim 14,characterized in that between said alignment control layer and saidsubstrate having said alignment control layer, there is an organic highmolecular layer having a thickness greater than that of said alignmentcontrol layer and which is transparent.
 17. A liquid crystal displayapparatus according to claim 16, characterized in that said organic highmolecular layer has an adhesion promotion agent which promotes a closeadhesion characteristic between said substrate face and said alignmentcontrol layer.
 18. A liquid crystal display apparatus according to claim16, characterized in that the thickness of said transparent organic highmolecular layer is 0.2-3 microns, and the thickness of said alignmentcontrol layer is 0.01-0.1 microns.
 19. A liquid crystal displayapparatus according to claim 16, characterized in that each of saidalignment control layer and said transparent organic high molecularlayer is comprised of polyimide.
 20. A liquid crystal display apparatusaccording to claim 19, characterized in that said transparent organichigh molecular layer is made by amorphous material.
 21. A liquid crystaldisplay apparatus according to claim 19, characterized in that saidtransparent organic high molecular layer is formed by heating it to atemperature where polyamic acid having a concentration of more than 8%is heated to proceed at least partially to an imidization.
 22. A liquidcrystal display apparatus according to claim 19, characterized in thatsaid alignment control layer is formed by coating where a solublepolyimide having a concentration of 0.5-6% or polyamic acid is coatedand by heating it to a temperature where at least a solvent agent isevaporated.
 23. A liquid crystal display apparatus according to claim18, characterized in that said transparent organic high molecular layeris made by amorphous material.
 24. A liquid crystal display apparatusaccording to claim 20, characterized in that said transparent organichigh molecular layer is formed by heating it to a temperature wherepolyamic acid having a concentration of more than 8% is heated toproceed at least partially to an imidization.
 25. A liquid crystaldisplay apparatus according to claim 20, characterized in that saidalignment control layer is formed by coating where a soluble polyimidehaving a concentration of 0.5-6% or polyamic acid is coated and byheating it to a temperature where at least a solvent agent isevaporated.